Process for producing ammoniated phosphatic fertilizers



United States Patent PROCESS FOR PRODUCING AMMONIATED PHOSPHATICFERTILIZERS John N. Carothers and Rudolph J. Hurlia, Jr., both of 1629Lady Marion Lane NE., Atlanta, Ga.

No Drawing. Filed Feb. is, 1955, Ser. No. 489,266 11 Claims. or. 71-40)This invention relates in general to a process for the production of afertilizer material, and more particularly to the production of a highlyavailable phosphate, in which neutralizing ammonia is added toacidulated phosphate rock, in such quantities as have heretofore beenconsidered impossible without the formation of substantial quantities ofobjectionable reverted or citrate insoluble P which is not available foruse as a fertilizer.

In this specification, by the term neutralizing ammonia we mean freeammonia, as contrasted with combined ammonia in a salt. And by generalexcess of ammonia we means an excess of that required to react with theacidic hydrogen. By acidulated phosphate rock we mean phosphate rock,prepared according to the method outlined in this disclosure. By theterm superphosp-hate We mean the product of commerce known by that nameand as heretofore produced by acidulating phosphate rock with sulfuricacid. Also, throughout this specification where parts are mentioned,parts by weight are intended. By the term available phosphate is meantthe total P 0 content of the product less the citrate insoluble P 0content.

The principal objects of this invention are to provide a process forproducing ammoniated phosphate, which shall be higher in ammonia contentthan hereto-fore obtained and be prepared by the addition ofneutralizing ammonia to acidulated phosphate rock in such a manher as toconvert substantial quantities of water soluble P 0 into water insolubleP 0 yet be in a form which is citrate soluble and available for use as afertilizer; also, to react the ammonia with substantially all of theacid required for acidulation of the phosphate rock, except thatrequired to react with the carbonates, fluorides and minor otherimpurities.

A further object of our invention is to produce an ammoniated phosphate,having a high available P 0 content, yet being low in calcium sulfatecontent and containing a minimum amount of acidic hydrogen.

Another object of our invention is to produce a phosphatic fertilizercontaining ammonium sulfate and calcium phosphate in which the calciumphosphate is water insoluble and citrate soluble and has approximatelythe ratio of Ca to P 0 found in tricalcium phosphate. v

A still further object of our invention is to add neutralizing ammoniaonly to acidulated phosphate rock, in such quantities that in the finalproduct, the units of ammonia per 20 units of P 0 may be in excess of11, and which shall contain only small quantities of unavailable P 0Another object of our invention is to provide a process in whichacidulated phosphate rock is ammoniated to a higher percentage ofammonia than heretofore achieved without first removing the fluorinecontained in the phosphate rock.

Another object of this invention is to provide a process of producingfrom phosphate rock, in the presence of substantially all the fluorineoriginally present in the rock, a product containing a higher percentageof ammonia than has heretofore been achieved and in which substantiallyall of the P 0 in the product is citrate soluble. V

And an additional object is the ammoniation of acidulated phosphate rockto form a citrate soluble phosphate, which shall be more basic thandicalcium phosphate, and which shall be formed along with the ammoniumsalt produced during the ammoniation.

The addition of neutralizing ammonia in appreciable quantities toordinary superphosphate dates from about 1929. The quantity ofneutralizing ammonia which is added, averages 2.5 parts per 20 parts P 0Kumagi et al., Journal of Agricultural and Food Chemistry, vol. 2,January 6, 1954. This article on page 25 states: However there is adearth of published information on ammoniation technique, optimumconditions forammoniation, and the influence of physical properties ofraw materials on ammonia absorption. A great deal of research has beenundertaken to find out just what reactions occur when ammonia is addedto ordinary superp'hosphate. Since the addition of ammonia was firstbegun commercially there has been only a limited increase in quantitiesof ammonia added per unit of P 0 and this increase has been attainedmainly through manipulative procedure, including the addition ofammonium salts, and not because of basic changes in the process, orcontrol of the reactions which cause reversion.

When the ammoniation of superphosphate was first begun, theinvestigators expressed the reactions in four principal equations asshown below, which are still generally accepted as representing whatoccurs'when ordinary superphosphate is fully ammoniated:

Heretofore in ammoniating ordinary superphosphatc it has been generallyregarded that dicalcium phosphate was formed from the water soluble P 0and such free acid as was present and that the formation of dicalciumphosphate represented the maximum possible ammonia addition withoutforming undesirable citrate insoluble P 0 commonly referred to astricalcium phosphate.

This opinion has found expression in many technical j calcium phosphateformed during the ammoniation of superphosphate, and upon furtherammoniation that citrate insoluble tricalcium phosphate is formed, asillustrated by Equations 2, 3 and 4, above, we believe there is evidencethat indicates that a water insoluble, available phosphate more basicthan dicalcium phosphate is formed at all stages of ammoniation ofacidulated phosphate rock.

A great deal of research work has been done in trying to determine thecauses of reversion of available phosphates to the citrate insolubleform. Some reports state that fluorine is the main cause of reversion,and the fluoapatite is formed, while others report the compound ofreverted P 0 as being hydroxy apatite. (Datin et al.,

Ind. and Eng. Chem, vol. 44, p. 903 et seq. (1952);

Hecht et al., Ind. and Eng. Chem, vol. 44, p. 11 19 et seq. (1952);Jacob et al., Ind. and Eng. Chem, vol. 22,

Patented Mar. 1961 p. 1385 (1930); Keenan, Ind. and Eng. Chem, vol. 22,p. 1378 (1930).)

Various proposals have been made to overcome reversion of P in theammoniation of supcrphosphate. For example, it has been proposed to addammonium salts, such as the sulfate and the nitrate and to cool theammoniated product before storage. Some of the most recent reportsconclude that the best way to avoid reversion is to remove the fluorinebefore ammoniation; however that conclusion is followed by the statementthat no economically feasible way to do so is known.

In the current manufacture of ordinary superphosphate it is the generalpractice to acidulate phosphate rock with sulfuric acid of such strengththat as the mix goes to the storage pile for curing it may contain asmuch as moisture. While curing it is customary to aerate the product bydropping the material from a considerable height either by means of dumpcars located on an elevated track near the top of the storage buildingor by dropping. it from a crane bucket. This facilitates the escape ofwater vapor and tends to cool the freshly prepared product. (Waggaman,Phosphoric Acid Phosphates and Phosphatic Fertilizers, Second Edition,page 270.) Acid of varying strengths are used, which generally rangebetween 50 and 56 B., being from 62% to 71% H 80 The variations in acidstrength, and the proportions of acid to rock, depend on the grade andkind of phosphate rock being acidulated, and also on the preferredoperating practice at a given plant.

In calculating acid requirements for superphosphate, as heretoforeproduced, consideration has been given to provide only sufiicient acidto make the P 0 in the rock available, part of which was Water soluble,and part of which water insoluble, yet citrate soluble. Shoed et al.,Ind. and Eng. Chem., vol. 41, page 1334 et seq. (1949); Marshall et al.,Ind. and Eng. Chem, vol. 32, p. 1128 (1940). Taking into considerationboth the cost of the acid used in the acidulation and the cost of thephosphate rock the process is operated in a way to keep the cost ofavailable P 0 at a minimum.

It has not been recognized heretofore that varying the ratio of acid torock when acidulating phosphate rock has any effect on the ammoniationof the superphosphate. Nor has it been recognized that varying the acidto phosphate rock acidulating ratio, has any effect on conditioning ofthe superphosphate for ammoniation, when curing conditions were alsovaried. The influence of temperature during ammoniation of acidulatedphosphate rock, likewise has never been fully appreciated.

We have discovered that while phosphate rock acidulated on the acid torock ratio used in making ordinary superphosphate may be ammoniated toan ammonia content higher than heretofore realized, while retaining highP 0 availability, there are advantages to ammoniating an acidulatedphosphate rock which is made with more than the minimum ratio ofacidulating acid to rock. We have discovered that by increasing the acidto phosphate rock ratio in acidulation, are able to add largerquantities of NH to the acidulated rock under conditions which cannot beused at lower ratios, and we are able to make a product in which thewater soluble frac tion of the P 0 is less, and thereby avoidundesirable ill effects which occur from soil reversion of water solubleP205.

In accordance with our improved process we may add as much as 9.2 partsNI-I to parts P 0 to phosphate rock acidulated on the acid to rock ratioused in making ordinary superphosphate and as much as 12 parts NH to 20parts P 0 to phosphate rock acidulated in the manner hereinafter setforth and produce a. product in which the P 0 is over 97% available.

The phosphate rock may be acidulated in conventionally used equipment bymixing the dry phosphate rock with sulfuric acid, which has been dilutedto a strength of from 60% to 75% H and which will give 3. moisturecontent of from 6% to 25% in the end product after aging; or thephosphate rock may be moistened with water, and a somewhat moreconcentrated acid may be used than would be the case if dry phosphaterock is acidulated.

For example, when using Florida pebble phosphate rock having 34% P 0 and3.7% F, we preferably use the equivalent of 70 pounds H 80; and 42pounds water, per 100 pounds phosphate rock or 2.06 pounds H 80 (100%basis) for 1 pound P 0 in the rock. This is 80% of the 2.57 pounds H 50per pound P 0 required to convert the P 0 in high grade rock tophosphoric acid. (Waggaman, Phosphoric Acid Phosphates and PhosphaticFertilizers, 2nd Edition, page 216). As will be shown in the specificexamples hereinafter set forth, a lesser proportion of acid to rock maybe employed. Of course it is obvious to those skilled in the manufactureof ordinary superphosphate, that various sizes of the mix and thetemperature of materials being used necessitate changes in the quantityof water used. We have found that these proportions of phosphate rockand acid give substantially complete solubilization of the phosphaterock, and renders the P 0 content of the rock substantially completelywater soluble with some free phosphoric acid. A still higher acid tophosphate rock ratio could be employed but it would be economicallyundesirable.

The acidulated mix should be aged for a week or longer either at atemperature which may be above 80 C., or at lower temperatures down toatmospheric temperature. As will be seen in the examples which follow,the temperature at which the mix is aged may vary the manner in which itmay later be ammoniated. After such aging it is ready for ammoniation.During the aging step we believe that substantial quantities of thefluorine in the rock react to form highly insoluble compounds, such asare described in our copending application Serial No. 424,931, filedApril 22, 1954, and now abandoned, which compounds are subsequentlyunaffected in the ammoniation. in any event the aging of the materialshould take place without substantial drying whereby it will containfrom 6% to 25% moisture after aging as set forth above.

When the acidulated mix is aged for one week or longer at a temperatureabove 80 C., it can then be ammoniated at a temperature below 70 C., andthe ammoniated product dried at temperatures in the neighborhood of 100C. immediately after ammoniation. A product is thus obtained containingup to 12.1 parts N11 per 20 parts P 0 in which the P 0 is about 98%available, and 1%2% water soluble.

When the acidulated mix is aged for a week or longer, at temperatures inthe neighborhood of atmospheric temperature, it can be ammoniated attemperatures below 70 C., and if allowed to react for a period ofseveral hours below 70 C., it can then be dried at any desiredtemperature, including temperatures in the neighborhood of 100 C. Aproduct is thus obtained containing up to 12.1 parts NH per 20 parts P 0in which the P 0 is about 98% available, and 12% water soluble. We haveallowed the material to react for a period of 1 hour and upon dryingobtained a product in which the P 0 was 94% available. Where thematerial reacted for 13 hours before being dried the P 0 was 98%available.

We have found that when the acidulated mix which has aged for a week orlonger at temperatures in the neighborhood of atmospheric temperature isheated or dried at temperatures in the neighborhood of 100 C.immediately after ammoniation, reversion of P 0 occurs. A product isthus obtained containing up to 12.2 parts NH per 20 parts P 0 in whichthe P 0 is only about available and about 1% water soluble. Higheravailability may be obtained from such material however, by the additionof approximately 12% calcium sulfate and 12% ammonitun sulfate to themixture before ammoniation.

We have carried out our improved process in many tests, examples ofwhich will be hereinafter described and have observed no ill effectsfrom a local excess of ammonia. For example, we have added ammonia untila general excess was present, and the resulting product had a high ratioof NH to P and a high percentage of available P 0 Heat is developed whenNH is added to acidulated phosphate rock. The extent to which theammoniated mass heats, depends upon the temperature of the startingmaterials, whether more or less water is evaporated, and upon the meansof ammoniation; for instance whether an ammoniating solution or gaseousammonia is used. It is obvious that the average temperature of the massis lower than the temperature in the region Where the ammoniationreaction occurs. In any event the temperature during ammoniation shouldnot be allowed to exceed 75 C.

We are unable to explain the reactions which take place, whereby suchlarge quantities of ammonia can be added to the acidulated phosphatewithout forming objectionable quantities of unavailable P 0Nevertheless,

.we have observed, by repeated'tests, that in carrying out our improvedprocess as herein outlined, 11 units and above of ammonia per units of P0 can be added without forming objectionable quantities of citrateinsoluble P 0 7 By means of our improved process, we are able to makemore efficient use of the sulfuric acid employed to solubilize thephosphate rock than has heretofore been attained in that we make anavailable phosphate, and convert the major portion of the sulfate in thecalcium sulfate into ammonium sulfate by the use of ammonia with theacidulated phosphate rock as will be shown by the examples hereinafterset forth.

We are enabled by means of our improved process to make a citratesoluble form of P 0 from the phosphate content of phosphate rock withthe net expenditure of less sulfuric acid than would be needed to makedicalcium phosphate from the tricalcium equivalent of the phosphaterock. This is brought about by the fact that we utilize the calciumsulfate as a source of sulfate to make ammonium sulfate and utilize themajor portion of the acid used in acidulating the phosphate rocksubsequently to react with ammonia. Accordingly, we not only make asuperior phosphate fertilizer, but obtain a great saving in rawmaterials.

In the examples which follow satisfactory ammoniation with a high NHcontent was obtained with acidulated phosphate rock prepared indifferent ways. These examples include comparisons of conditions duringthe ammoniation of acidulated phosphate rock aged at temperatures above80 C., with those during ammoniation of acidulated phosphate rock agedat atmospheric temperature. Also included are comparisons of methods ofammoniating acidulated phosphate rock, prepared with various ratios ofacid to P 0 In all of the examples which follow the average temperatureof the mass during ammoniation was not allowed to exceed 75 C.

Example 1 a temperature between 8595 C.

To the above aged mixture, cooled to approximately C. immediately beforeammoniation, 27% aqua ammonia was added in an amount so that the finaldry product contained 9.8% ammonia, and had a total of 12.0 parts NH per20 parts P 0 The P 0 in the :final dry product was 97.9% available and1.5% water soluble. .acidulate the'phosphate rockvwas subsequentlyutilized In this example 84% of the H 80 used to to react with ammonia.After ammoniation the mixture was heated for about 4.5 hours in theneighborhood of? 100 C. during which time the excess water wasevaporated. It Will thus be seen that under conditions here toforeconsidered adverse there was no appreciable reversion of the P 0 tocitrate insolubility.

Example 2. The following mixture was prepared:

101.6 parts acidulated phosphate rock prepared in the preferred mannerhereinbefore outlined, containing 18% moisture and 1.75% fluorine, andaged at room temperature.

12.0 parts ammonium sulfate, and

12.6 parts calcium sulfate, dihydrate.

To the above mixture ammonia was added, as 28% aqua, in an amount sothat the resultant dry product contained 10.6% NH and had a total of 15parts ammonia to 20 parts P 0 of which 11.4 parts NH to 20 parts P 0 wasadded as free ammonia. The P 0 in the product was over 99% available,and 3.2% water soluble.

In adding the ammonium sulfate, 3 parts were dissolved in the aquaammonia before it was added to the acidulated phosphate rock. Thecalcium sulfate was all thoroughly mixed into the acidulated phosphaterock before the ammonia was added. After the ammonia was added to themixture it was heated in the neighborhood of l00 C. for about 1 hour,and the excess water was then evaporated. It will thus be seen thatalthough heated for a considerable period of time at a high moisture,high ammonia content, there was no material reversion. a

The amount of ammonia thus added was sufiicient to neutralizesubstantially all of the acidic hydrogen in the mixture. It will beapparent however that lesser amounts of ammonia may be employed where afinal product of lower ammonia content is being made.

Example 3 was added in an amount to provide NH in excessof that requiredto react with the acidic hydrogen in the mixture. The temperature wasmaintained below about 60 C. during the ammonia addition. The mixturestood 48 hours in the presence of the excess NH at temperatures in theneighborhood of atmospheric temperature. It was then dried attemperatures in the neighborhood of 45 'C. The P 0 in the final driedproduct was 99.4% available and 3.9% water soluble. the final driedproduct was 11.7 parts NH per 20 parts P 0 In this example approximately82% of the acid used to acidulate the phosphate rock was subsequentlyutilized to react with NH It will thus be seenthat,

although'the mixture was subjected to excess ammonia for a considerableperiod of time, a condition heretofore considered adverse, there wasobtained a product having a higher ammonia content with higheravailability than heretofore considered possible.

Example 4 I To acidulated phosphate rock, prepared in the preferredmanner hereinbefore outlined, containing 15% ture, it. was divided intotwo' portions One portion of The NH; content of I The temperature wasmaintained below about '55 the mixture was heated to and dried at atemperature in the neighborhood of 100 C. The P in the final driedproduct was 97.5% available and 1.5 water soluble. The ammonia contentof the final dried product was 12.1 parts NH per 20 parts P 0 in thisexample approximately 85% of the acid used to acidulate the phosphaterock was subsequently utilized to react with NH The second portion ofthe ammoniated material was heated to and dried at a temperature in theneighborhood of 45 C. The P 0 in the final dried product was 99%axailable and 2.5% water soluble. The ammonia content of the final driedproduct was 11.5 parts N11 per 20 parts P 0 In this exampleapproximately 81% of the acid used to acidulate the phosphate rock wassubsequently utilized to react with NH Example 5 Phosphate rock wasprepared in the preferred manner hereinbefore outlined, except that theconcentration of the sulfuric acid used for the acidulation was 74.7%.The acidulatcd rock contained 8.3% moisture and 18.4% P 0 after beingaged 29 days at temperatures between 85 C. and 95 C. To this materialcooled to approximately 40 C. immediately rior to ammoniation 27% aquaammonia was added in an amount to provide NH in excess of that requiredto react with the acidic hydrogen in the mixture. Immediately afterammoniation, the mixture was divided into two portions, one being heatedto and dried at temperatures in the neighborhood of 100 C. and the otherat temperatures in the neighborhood of 45 C. In the portion dried atabout 100 C. the P 0 in the final dried product was 98% available and1.3% water soluble. The ammonia content of the final dried product was12.1 parts NH per 20 parts P 0 Thus approximately 85% of the acid usedin acidulating the phosphate rock was subsequently utilized to reactwith N11 In the portion dried at about 45 C. the P 0 in the final driedproduct was 99% soluble. The ammonia content of the final dried productwas 11.9 parts NH per 20 parts P 0 Thus approximately 83% of the acidused in acidulating the phosphate rock was subsequently utilized toreact with NH It will thus be seen that acidulated phosphate rock, agedat temperatures between 85 and 95 C. and ammoniated at temperaturesbelow 70 C., may be heated to a temperature of around 100 C. driedimmediately after ammonlation without material reversion.

Example 6 Phosphate rock was acidulated in the manner set forth inExample 5 and contained 7.4% moisture and 18.6% P 0 after being aged 41days at temperatures between 85 C. and 95 C. To this material, cooled toabout 42 C. immediately prior to ammoniation, 27% aqua ammonia was addedin an amount somewhat less than that of Example 5. Immediately afterammoniation, the material was divided into two portions, one beingheated to and dried at temperatures in the neighborhood of 100 C. andthe other at a temperature in the neighborhood of 45 C. In the portiondried at about 100 C, the P 0 in the final dried product was 97.5%available and 19.9% water soluble. The ammonia content or" the finaldried product was 10.1 parts NH per 20 parts P 0 Thus approximately 71%of the acid used in acidulating the phosphate rock was subsequentlyutilized to react with NH In the portion dried at about 45 C., the P 0in the final dried product was 98.7% available and 19% water soluble.The ammonia content of the final dried product was 10.1 parts NR per 20parts P 0 Thus approximately 71% of the acid used in acidulating thephosphate rock was subsequently utilized to react with NH The foregoingresults, in comparison, with those of.

available and 1.5% water Example 5 shows the etlect of the smallerquantity of NH in the final dried product on the water solubility ofthe'P O of the product and that our process may be carried out as wellwith a smaller quantity of ammonia as with an excess of ammonia.

Example 7 To acidulated phosphate rock, prepared in the preferred mannerhereinbefore outlined, and containing 15% moisture and 17.1% P 0 afterbeing aged at atmospheric temperature for 26 days, 27% aqua ammonia wasadded in an amount to provide NH in excess of that required to reactwith the acidic hydrogen in the mixture. The temperature was maintainedbelow about 55 C. during the ammonia addition. Immediately afterammoniation the mixture was heated to and dried at about 100 C. The P 0in the final dried product was only 91.6% available and 0.7% watersoluble. The ammonia content of the final dried product was 12.2 partsNH per 20 parts P 0 Thus approximately of the acid used in acidulatingthe phosphate rock was subsequently utilized to react with NH Theresults in this example show the ill effect of high temperatureimmediately after ammoniation when using an acidulated phosphate rockaged at atmospheric temperature in contrast with the results obtained inExamples 3 and 4 where the ammoniated mixture was allowed to stand for aconsiderable period of time before drying. The results may also becompared with those obtained in Example 5 where the material was aged attemperatures of from 85 C. to C. and was heated to a temperature of C.immediately after ammoniation with no appreciable reversion.

Example 8 Phosphate rock was acidulated in the preferred mannerhereinbefore outlined, and contained 12.5% moisture and 17.9% P 0 afterbeing aged 18 days at temperatures between 85 C. and 95 C. To thismaterial after being cooled to approximately 40 C., 27% aqua ammonia wasadded in an amount to provide NH in excess of that required to reactwith the acidic hydrogen in the mixture. After the mixture stood 48hours in the presence of the excess NH it was dried at about 45 C. The P0 in the final dried product was 99.2% available and 5.1% water soluble.The ammonia content of the final dried product was 11.4 parts NH per 20parts P 0 Thus 80% of the acid used to acidulate the phosphate rock wassubsequently utilized to react with NH In this example in contrast withExample 5, the ammoniated product was allowed to stand for two days inthe presence of. an excess of ammonia without appreciable reversion.

Example 9 Phosphate rock was acidulated in the preferred mannerhereinbefore outlined, and was aged at atmospheric temperature for 34days. To this material 27% aqua ammonia was added in an amount toprovide about one-third of the total NH to be added. The partiallyammoniated product was placed in a closed vessel and NH gas was added.During the gaseous ammoniation, the temperature of the mass was keptbelow about 40 C. After ammoniation the product was dried at about 45 C.The P 0 in the final dried product was 99.6% available and 7.1% watersoluble. The ammonia content of the final dried product was 11.2 partsNH per 20 parts P 0 Thus 78% of the acid used in acidulating thephosphate rock was subsequently utilized to react with NH This exampledemonstrates that our improved process may be carried out equally wellwith aqueous ammonia or gaseous ammonia.

It will also be apparent from the preceding examples that whatever thecauses of reversion in prior art processes which were attributed toexcess moisture, or over ammoniation, such factors do not affect theavailability of the P 0 in our improved process.

The superphosphate of commerce is generally made by acidulatingphosphate rock with sulfuric acid on a weight ratio ranging between 1.77and 1.91 parts H 80 (100% basis) per part P contained in high gradephosphate rock or from 60 to 65 pounds H 80 to 100 pounds high gradephosphate rock.- The P 0 in such a product is substantially completelyavailable and upwards of 85% water soluble. We have discovered that suchacidulated phosphate rock, may be successfully ammoniated in accordancewith our improved process to an ammonia content of from 9 to 10 parts NHper 20 parts P 0 with the P 0 content of the product being up to 99%available.

In the examples which follow, we set forth the manner in which thisammoniation may be accomplished. Later we give an example of the resultsif improper conditions are employed.

' Example 10 To an acidulated phosphate rock, prepared with 50 B.sulfuric acid, using 1.77 parts H SO (100% basis) per one part P 0 inhigh grade phosphate rock (or 60 pounds H 50 to 100 pounds of rock) andaged 60 days at atmospheric temperature, 27% aqua ammonia was added inan amount to provide NH in excess of that required to react with theacidic hydrogen in the mixture. During the ammoniation the temperaturewas kept between 50 and 55 C., and higher temperatures were prevented byevaporation of water. The ammoniated mixture stood 72 hours atatmospheric temperature in the presence of the excess ammonia and wasthen dried at a temperature below 45 C. The P 0 in the final driedproduct was 99% available and 4.9% water soluble. The ammonia content ofthe final dried product was 9.5 parts NH per 20 parts P 0 Thus about 77%of the acid used in acidulating the phosphate rock was subsequentlyutilized to react with NH In another case in which the ammoniatedmixture stood 48 hours after ammoniation and before drying the P 0 ofthe final dried product was over 99% available and 5% water soluble. Thefinal dried product in this case had an ammonia content of 9.2 parts NHper 20 parts P 0 Thus about 75% of the acid used in acidulating thephosphate rock was subsequently utilized to react with Example 11 To anacidulated phosphate rock, prepared with 50 B. sulfuric acid using 1.77parts H 50 (100% basis) per one part P 0 (or 60 parts H 80 to 100 partshigh grade phosphate rock) and aged 18 days at temperatures between 85and 95 C., and cooled to approximately 40 C. immediately prior toammoniation, 27% aqua ammonia was added in an amount to provide NH inexcess of that required to react with the acidic hydrogen in themixture. During the ammoniation the temperature was kept between 50 and55 C. and higher temperatures were prevented by evaporation of water.Immediately after ammoniation, the mixture was heated to and dried atabout 100 C. The P 0 in the final dried product was only 82% available,and was 22.5% water soluble. The NH content of the final dried productwas only 7.4 parts NH per 20 parts P 0 Thus only about 60% of the acidused in acidulating the phosphate rock was subsequently utilized toreact with NH;.;, and the loss of availability of the P 0 was high. Inthis example where the acid to phosphate rock ratio is that employed inmaking ordinary superphosphate, although there was a general excess ofNH the reaction of the acidulated phosphate rock with the NH gave adisproportionately lower ammonia content of the product, expressed asparts NH per 20 parts P 0 than in Example 1, where a higher ratio ofacid to rock was employed. Furthermore there was considerable reversionin this example and practically none in Example 1. This example showsthat phosphate rock acidulated with Example 12 Acidulated phosphaterock, made with 50 B. sulfuric acid using 1.77 parts H 50 100% basis)per one part P 0 or parts H 80 to 100 parts high grade phosphate rock,containing 17.8%

ammoniated with anhydrous ammonia gas.

The NH; was added at a rate which permitted keeping the mass below about45 C., and was absorbed during a period of about four hours. The masswas stirred intermittently during the ammoniation. Immediately after'ammoniation a portion was dried at a temperature of about 45 C. The P 0in the dried product was over The ammonia content of the product was 8.5parts NH per 20 parts 4 P205.

99% available and 9.9% 'water soluble.

A second portion of the ammoniated mixture was kept in contact with theammonia at atmospheric tem-- perature for 60 hours and then dried atabout 45 C. The P 0 in this portion was over 99% available and 7.9%water soluble. tion was 9.0 parts NH per 20 parts P 0 A third portion ofthe ammoniated mixture was kept in an ammonia atmosphere at atmospherictemperature for 40 days, and then dried at about 45 C. The P 0 in thefinal dried product was about 97% available and 5.2% water soluble.product was 9.2 parts NH per 20 parts P 0 In all of the foregoingexamples, the acidulated phosphate rock contained substantially all thefluorine originallypresent in the rock which before acidulation averagedmore than 3%. The only reduction in fluorine content was that normallyoccurring during acidulation.

- While in all the foregoing examples we have used aqua ammonia orgaseous amomnia as the ammoniating agent it will be obvious to thoseskilled in the art that so called ammoniating solutions containingammonia as well as other nitrogen compounds may be employed in ourimproved process and that the ammonia contained in such solutions willreact with the phosphatic mixture in a similar manner to that hereindescribed.

From the foregoing it will be seen that by aging the acidulatedphosphate rock for a sufiicient length of time and controlling thetemperature of aging and during ammoniation and subsequent drying themaximum absorption of ammonia without reversion is obtained. It willalso be seen that still more favorable results are'obtained where theratio of H 80 to phosphate rock in.

acidulation is such as to render substantially" all the P 0 watersoluble. Further, it will be observed that under certain conditionsanother important factor is the proper aging of the ammoniated productbefore drying.

While we have described several ways in which our improved process maybe successfully carried out, it will be obvious to those skilled in theart that it is not so limited but that it is susceptible of variouschanges and modifications without departing from the spirit thereof,

and we desire, therefore, that only such limitations shall be placedthereupon as are set forth in the appended claims.

What we claim is:

1. The process of producing ammoniated phosphate in which substantiallyall of the P 0 is available from acidulated phosphate rock in thepresence of fluorine remaining in the rock after acidulation whichcomprises, acidulating the rock with sulfuric acid in the proportion of1.77 pounds to 2.06 pounds H to each pound of P 0 in the rock and withmoist product, allowing the acidulated rock to age without substantialdrying for at least a week, whereby itwill contain after aging in excessof 6% moisture, and adding P 0 and 17.6% moisture after being aged 133days at atmospheric temperature was The ammonia content of this por--The ammonia content of the dried suflicient water to form a ammonia tothe acidulated rock to produce a product having in excess of 6.5 partsammonia to 20 parts P while maintaining the temperature duringammoniation below 75 C.

2. A process as set forth in claim 1 in which the acidulated rock isaged at a temperature above 80 C.

3. The process of producing a fertilizer containing essentially ammoniumsulfate and citrate soluble calcium phosphate more basic than dicalciumphosphate which comprises acidulating phosphate rock with sulfuric acidto convert substantially all the P 0 to .water soluble form and withsufficient water to form a moist product, aging the acidulated productwithout substantial drying for at least a week whereby after aging theproduct contains in excess of 6% moisture, and adding ammonia to reactwith substantially 80% of the acid employed to acidulate the rock whilemaintaining the temperature of the mix below 75 C.

4. A process as set forth in claim 4 in which the product is ammoniatedto the extent that the ratio of Ca to P 0 in the calcium phosphate issubstantially that in tricalcium phosphate.

5. The process of producing a fertilizer containing essentially ammoniumsulfate and citrate soluble calcium phosphate more basic than dicalciumphosphate which comprises acidulating phosphate rock containing fluorinewith sulfuric acid of 55% to 75% H 80 in an amount to produce a moistmixture in which over 85% of the P 0 in the rock is converted to watersoluble phosphate, aging the moist mixture for at least a week withoutsubstantial drying whereby after aging it contains from 6% to 25%moisture, at a temperature in the neighborhood of 80 C., cooling themixture, adding ammonia up to 12 parts by weight to parts by weight of P0 in the product while maintaining the temperature below .75" C., anddrying.

6. The process of producing a phosphatic fertilizer in which the P 0 issubstantially 'all available which comprises acidulating phosphate rockcontaining fluorine with sulfuric acid in the presence of water in anamount to produce a moist product in which substantially all the P 0 inthe rock is converted to water soluble phosphate, aging the product forat least a week at a temperature in the neighborhood of 80 C., therebeing from 6% to moisture in the product after aging, adding ammonia inthe presence of the fluorine remaining in the acidulated rock whilemaintaining the temperature below 75 C. and in an amount sufficient toproduce a product comprising essentially citrate soluble calciumphosphate more basic than dicalcium phosphate and ammonium sulfate, anddrying the product at a temperature of from 45 C. up to the neighborhoodof 100 C.

7. The process of producing an ammoniated phosphatic fertilizer in whichthe P 0 content is substantially all available from phosphate rockhaving approximately 34% P 0 and containing 3% or more fluorine whichcomprises reacting approximately pounds sulfuric acid with 100 poundsphosphate rock in the presence of sufiicient \vaterto produce a moistmixture in which the P20 is substantially all water soluble, aging themixture without substantial drying at a temperature in the neighborhoodof C. for at least a week, there being from 6% to 25% moisture in themixture after aging, cooling the mixture to a temperature below 75 0.,adding ammonia to the fluorine containing mixture in an amount up tothat sufficient to neutralize all of the acidic hydrogen in the mixturewhile maintaining the temperature below 75 C., and drying the product.

8. A process for the production of ammoniated phosphate fertilizer ofhigh P 0 rock containing around 30% to 35% P 0 which comprisesacidulating the rock with sulfuric acid in the proportions of from 60 to75 pounds H 50 to 100 pounds of phosphate rock in the presence ofsufficient water to form a moistmixture, aging the acidulated mixwithout substantial drying for at least a Week, whereby after aging themixture contains from 6% to 25% moisture, cooling the mixture to atemperature below 75 C., adding ammonia to the aged mix in an amountfrom 6.5 parts per 20 parts P 0 up to an amount to react withsubstantially all of the acidic. hydrogen therein while maintaining themixture at a temperature below 75 C., and drying the mixture.

9. A process. as set. forth in claim 8 in which the acidulated productis aged at a temperature of from to C., and after ammoniation is driedat temperatures up. to C.

10. A process as set forth in claim 9 in which the aged acidulatedphosphate rock is cooled to a temperature in the neighborhood of 40 C.before ammoniation.

11. A process as set forth in claim 9 in which around 12 parts per 100each of calcium sulfate and ammonium sulfate were. added to theacidulated phosphate rocl; before ammoniation.

References Cited in the file of this patent UNITED STATES PATENTS709,185 Terne Sept. 16, 1902 1,122,183 Willson et a1. Dec. 22, 19141,870,602 Case Aug. 9, 1932 1,930,883 Oehme Oct. 17, 1933 2,060,310Harvey Nov. 10, 1936 2,077,171 Harvey Apr. 13, 1937 2,116,866 KniskernMay 10, 1938 2,136,793 Gabeler et a1 Nov. 15, 1938 availability fromphosphate UNITED STATES PATENT OFFICE CERTIFHIATION OF CORRECTION PatentNo. 2,976, 140 March 21 1961 John N Carothers et ale It is herebycertified that error appears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

Column 11, line l9 for the claim reference numeral "4:" read 3 column l2line 35, for the claim reference numeral "'9'7- read 8 line 38,, for theclaim reference numeral '9". read 8 Signed and sealed this 29th day ofAugust 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

1. THE PROCESS OF PRODUCING AMMONIATED PHOSPHATE IN WHICH SUBSTANTIALLYALL OF THE P2O5 IS AVAILABLE FROM ACIDULATED PHOSPHATE ROCK IN THEPRESENCE OF FLUORINE REMAINING IN THE ROCK AFTER ACIDULATION WHICHCOMPRISES, ACIDULATING THE ROCK WITH SULFURIC ACID IN THE PROPORTION OF1.77 POUNDS OF 2.06 POUNDS H2SO4 TO EACH POUND OF P4O5 IN THE ROCK ANDWITH SUFFICIENT WATER OF FROM A MOIST PRODUCT, ALLOWING THE ACIDULATEDROCK TO AGE WITHOUT SUBSTANTIALLY DRYING FOR AT LEAST A WEEK, WHEREBY ITWILL CONTAIN AFTER AGING IN EXCESS OF 6% MOISTURE, AND ADDING AMMONIA TOTHE ACIDULATED ROCK TO PRODUCE A PRODUCT HAVING IN EXCESS OF 6.5 PARTSAMMONIA TO 20 PARTS P2O5 WHILE MAINTAINING THE TEMPERATURE DURINGAMMONIATION BELOW 75*C.